Call establishment and maintenance in a wireless network

ABSTRACT

Techniques to configure quality of service (QoS) and utilize radio resources for a call in a WLAN are described. In an aspect, a station ensures that an access point in the WLAN is suitable for receiving service prior to performing registration to receive services via the WLAN. In another aspect, the station first requests for radio resources for traffic flows, then requests for radio resources for signaling flows, and sends signaling as best effort traffic if radio resources are not granted for the signaling flows. In yet another aspect, the station aggregates QoS for multiple applications and requests for radio resources based on the aggregated QoS. In yet another aspect, the station releases extra radio resources corresponding to the difference between the QoS granted by the WLAN and the QoS proposed by a remote terminal for the call. In yet another aspect, the station requests for the same QoS or lower from a new access point during handoff.

The present application for patent is a Divisional and claims priorityto patent application Ser. No. 11/777,210, filed Jul. 12, 2007, entitled“CALL ESTABLISHMENT AND MAINTENANCE IN A WIRELESS NETWORK,” and claimspriority to Provisional U.S. Application No. 60/831,004, filed Jul. 14,2006, entitled “VOICE OVER IP FOR WIRELESS LOCAL AREA NETWORK”, andassigned to the assignee hereof and hereby expressly incorporated byreference herein.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for establishing and maintaining a call in awireless network.

II. Background

Wireless communication networks are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These wireless networks include wireless wide areanetworks (WWANs), wireless metropolitan area networks (WMANs), andwireless local area networks (WLANs). The terms “network” and “system”are often used interchangeably.

A user may utilize a station (e.g., a cellular phone) to obtain adesired service (e.g., voice) from a wireless network. The desiredservice may be satisfactorily provided to the user by ensuring that therequired quality of service (QoS) can be achieved for the service. Therequired QoS may be quantified by different parameters for differentservices and/or different wireless networks. For example, voice servicemay require a relatively stringent delay, a certain minimum guaranteeddata rate, and a certain frame error rate (FER) or packet error rate(PER) for satisfactory performance.

The station may exchange signaling with the wireless network in order toconfigure QoS for the desired service. The wireless network may grantsufficient radio resources to meet the QoS for the desired service. Itis desirable to efficiently configure QoS and utilize radio resourcesfor a call for the desired service.

SUMMARY

Techniques to efficiently configure QoS and utilize radio resources fora call in a wireless network are described herein. In an aspect, astation ensures that an access point in a WLAN is suitable for receivingservice prior to performing registration to receive services via theWLAN or to move services over to the WLAN. The station may detect foraccess points in the WLAN and may determine whether any detected accesspoint is suitable for receiving service, e.g., based on FER of beaconframes received from an access point and/or received signal strengthindicator (RSSI) measurements for the access point. The station mayperform service registration after determining a suitable access pointfor receiving service.

In another aspect, the station may first request for radio resources forat least one traffic flow and may receive a first grant of radioresources for the traffic flow(s). The station may then request forradio resources for at least one signaling flow. The station maycommunicate via the traffic and signaling flows regardless of whether ornot radio resources are granted for the signaling flow(s). The stationmay send data for the traffic flow(s) with the first grant of radioresources. The station may send signaling for the signaling flow(s) withradio resources granted for the signaling flow(s), if any, or as besteffort traffic if no radio resources are granted.

In yet another aspect, the station may determine QoS for each ofmultiple applications and may aggregate the QoS for these applications.The station may then request for radio resources from the WLAN based onthe aggregated QoS for these applications. The station may update theaggregated QoS whenever a new application is added or an existingapplication is removed. The station may then request for radio resourcesfor the updated aggregated QoS.

In yet another aspect, the station may determine the QoS granted by theWLAN and the QoS for a media format proposed by a remote terminal forthe call. The station may release extra radio resources corresponding tothe difference between the QoS granted by the WLAN and the QoS for themedia format proposed by the remote terminal.

In yet another aspect, the station may communicate with the remoteterminal based on a first QoS granted by a first access point. Thestation may perform handoff from the first access point to a secondaccess point. The station may request for the first QoS or lower fromthe second access point and may receive a grant of the first QoS orlower from the second access point. The station may then communicatewith the remote terminal based on the first QoS or lower granted by thesecond access point. This avoids causing the remote terminal tore-negotiate QoS.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a WLAN, a 3GPP network, and a 3GPP2 network.

FIG. 2 shows data flows and streams at various layers.

FIG. 3 shows a message flow for a VoIP call/session by a station.

FIG. 4 shows a process performed by the station for serviceregistration.

FIG. 5 shows a message flow for mobile-originated call setup.

FIG. 6 shows a message flow for mobile-terminated call setup.

FIG. 7 shows a process for requesting radio resources.

FIG. 8 shows a process for aggregating QoS for multiple applications.

FIG. 9 shows a process for relinquishing extra radio resources.

FIG. 10 shows a process for establishing QoS during handoff.

FIG. 11 shows a process for placing an emergency call.

FIG. 12 shows a block diagram of the station.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelessnetworks such as WWANs, WMANs, and WLANs. A WWAN may be a Code DivisionMultiple Access (CDMA) network, a Time Division Multiple Access (TDMA)network, a Frequency Division Multiple Access (FDMA) network, anOrthogonal FDMA (OFDMA) network, a Single-Carrier FDMA (SC-FDMA)network, etc. A CDMA network may implement a radio technology such ascdma2000, Universal Terrestrial Radio Access (UTRA), etc. cdma2000covers IS-2000, IS-95 and IS-856 standards.

UTRA includes Wideband CDMA (W-CDMA) and Low Chip Rate (LCR). A TDMAnetwork may implement a radio technology such as Global System forMobile Communications (GSM). An OFDMA network may implement a radiotechnology such as Evolved UTRA (E-UTRA), IEEE 802.20, Flash-OFDM®, etc.A WMAN may implement a radio technology such as IEEE 802.16. A WLAN mayimplement a radio technology such as IEEE 802.11, Hiperlan, etc. Thesevarious radio technologies and standards are known in the art. UTRA,E-UTRA and GSM are described in documents from an organization named“3rd Generation Partnership Project” (3GPP). cdma2000 is described indocuments from an organization named “3rd Generation Partnership Project2” (3GPP2). For clarity, certain aspects of the techniques are describedbelow for a WLAN that implements IEEE 802.11.

FIG. 1 shows a deployment of a WLAN 100, a 3GPP network 102, and a 3GPP2network 104. A station (STA) 110 may communicate with WLAN 100 to obtainvarious communication services supported by WLAN 100, 3GPP network 102,and/or 3GPP2 network 104. Station 110 may also be referred to as amobile station, a user equipment (UE), a terminal, a user terminal, asubscriber unit, etc. Station 110 may be a cellular phone, a personaldigital assistant (PDA), a wireless modem, a handheld device, a laptopcomputer, etc. Station 110 may communicate or exchange data with otherterminals and/or servers (e.g., a remote terminal 180) via WLAN 100.

WLAN 100 includes access points 120 a and 120 b and a Network AddressTranslation (NAT) firewall/router 130. Each access point 120 providesaccess to distribution services via the wireless medium/channel forstations associated with that access point. Router 130 routes packetsbetween access points 120 and the Internet 150 and may performtranslation between private and public Internet Protocol (IP) addressesfor the access points and stations within WLAN 100. WLAN 100 mayimplement any standard in the IEEE 802.11 family of standards. WLAN 100may also implement IEEE 802.11e, which covers QoS enhancements for aMedium Access Control (MAC) layer.

3GPP network 102 may be a Universal Mobile Telecommunication System(UNITS) network that utilizes W-CDMA or a GSM network. In 3GPP network102, a Node B 122 supports radio communication for UEs (not shown). ABase Station Subsystem (BSS)/Radio Network Controller (RNC) 132 controlsthe use of radio resources and performs other functions. A Serving GPRSSupport Node (SGSN) 142 supports transfer of packets to and from the UEsserved by the SGSN and may perform functions such as packet routing,access control, mobility management, security, etc. A Gateway GPRSSupport Node (GGSN) 142 interfaces with an intranet 152 and may performfunctions such as packet routing, IP address assignment, authentication,billing, etc. A Packet Data Gateway (PDG)/WLAN Access Gateway (WAG) 162allows UEs to access services from 3GPP network 102 via WLANs and mayperform various functions such as user authentication, secure tunnelmanagement, etc. A Call Session Control Function (CSCF) 172 may includea Proxy CSCF (P-CSCF), a Serving CSCF (S-CSCF), an Interrogating CSCF(I-CSCF), etc. CSCF 172 performs various functions to support IPMultimedia Subsystem (IMS) services such as Voice-over-IP (VoIP),multimedia, Short Message Service (SMS) over IP, Instant Messaging (IM),push-to-talk (PTT), etc. CSCF 172 may process requests from UEs for IMSservices, perform registration for IMS, provide session controlservices, maintain session state information, etc.

3GPP2 network 104 may be a CDMA2000 1× network that utilizes IS-2000 orIS-95, a High Rate Packet Data (HRPD) network that utilizes IS-856, etc.In 3GPP2 network 104, a base station 124 supports radio communicationfor mobile stations (not shown). A Base Station Controller (BSC)/PacketControl Function (PCF) 134 provides coordination and control for thebase stations under its control and routes data for these base stations.A Packet Data Serving Node (PDSN) 144 supports data services for themobile stations in 3GPP2 network 104 and may perform functions such asdata session establishment, maintenance, and termination, packetrouting, IP address assignment, etc. A Packet Data Interworking Function(PDIF) 164 provides IP connectivity to 3GPP2 network 104 and may performvarious functions such as user authentication, secure tunnel management,IP address allocation, packet encapsulation and de-capsulation, etc.CSCF 174 performs various functions to support IMS services.

Wireless networks 100, 102 and 104 may include other network entitiesnot shown in FIG. 1. Wireless networks 100, 102 and 104 may coupledirectly or indirectly to other networks such as a Public SwitchedTelephone Network (PSTN) 178 that serves conventional telephones.Station 110 may communicate with other terminals and servers that maycommunicate with any of the networks.

FIG. 2 shows flows and streams at various layers for station 110 whencommunicating with WLAN 100. Station 110 may have one or moreapplications that may engage any communication services. Theapplications may be for VoIP, video, packet data, etc. The applicationsmay communicate with other entities (e.g., remote terminal 180) usingSession Initiation Protocol (SIP), Real-time Transport Protocol (RTP),and/or other protocols at an application layer. SIP is a signalingprotocol for creating, modifying, and terminating sessions for VoIP,multimedia, etc. RTP provides end-to-end network transport functions andis suitable for applications sending real-time data such as voice,video, etc. Each application may have any number of data flows. A dataflow may be a SIP flow, an RTP flow, a best effort (BE) flow, etc. Forexample, a VoIP application may have one or more RTP flows for trafficdata and a SIP flow for signaling. As another example, application 1 maybe a SIP application having a SIP flow. Applications 2 through N may beSIP-based applications, each of which may have one or more data flowsfor traffic data and may send signaling via the SIP flow for application1.

The data flows may be processed by a data layer and mapped to IP flows.The data layer may include Transmission Control Protocol (TCP), UserDatagram Protocol (UDP), IP and/or other protocols. For example, station110 may have one IP flow to carry RTP and SIP flows for a VoIPapplication and may have another IP flow to carry a best effort flow fora browser application.

In IEEE 802.11e, the IP flows may be processed by the MAC layer andmapped to traffic streams. Each traffic stream may be associated with atraffic classification (TCLAS) and/or a traffic specification (TSPEC).The TCLAS specifies parameters used to identify MAC service data units(MSDUs) belonging to the traffic stream so that these MSDUs can be sentin accordance with the TSPEC for the traffic stream. The TSPEC describestraffic attributes (e.g., MSDU sizes and arrival rates) and trafficcharacteristics (e.g., data rate, maximum delivery delay, maximum delayvariance or jitter, etc.) of the traffic stream. Some or all of theparameters for the TSPEC may be considered as QoS parameters that may beused to define QoS.

IEEE 802.11e supports enhanced distributed channel access (EDCA), whichallows for prioritized access to the wireless medium/channel by stationsbased on QoS requirements of the flows carried by these stations and theamount of traffic through the stations. EDCA utilizes the followingaccess parameters for controlling access and transmission on the channelby the stations.

-   -   Arbitration inter frame space (AIFS)—amount of time to wait for        the channel to be idle before transmission may occur,    -   Minimum and maximum contention windows (CWmin and CWmax)—amount        of time to wait when the channel is detected to be busy, and    -   Transmission opportunity (TXOP) limit—maximum amount of time a        station can transmit on the channel upon gaining access.

To access the channel, station 110 may first sense the channel to see ifthe channel is idle or busy. If the channel is idle for AIFS time, thenstation 110 may transmit on the channel. If the channel is busy, thenstation 110 may wait until the channel becomes idle, then wait for thechannel to remain idle for AIFS time, and then select a random backoffbetween zero and a contention window, which may be set to CWmininitially. The random backoff is used to avoid a scenario in whichmultiple stations transmit simultaneously after sensing the channel idlefor AIFS. Station 110 may then count down the random backoff, pausingwhenever the channel is busy, and restarting the countdown after thechannel is idle for AIFS. Station 110 may transmit on the channel whenthe countdown reaches zero. Station 110 may double the contention windowafter each unsuccessful transmission until the contention window reachesCWmax.

AIFS is the amount of time that station 110 waits after the channelbecomes idle following a busy period. Station 110 defers access to thechannel during AIFS time. AIFS may thus affect the likelihood of gainingaccess to the channel. In general, a station with higher prioritytraffic may use a smaller AIFS value to allow for access of the channelbefore other stations with lower priority traffic and hence larger AIFSvalues. The minimum contention window and (to a lesser extent) themaximum contention window may determine the average amount of time toaccess the channel. A station with a smaller CWmin may, on average, gainaccess to the channel in a shorter amount of time than a station with alarger CWmin.

IEEE 802.11e supports four access categories—voice (AC_VO), video(AC_VI), best effort (AC_BE), and background (AC_BK). The four accesscategories have a total of eight different priorities, with each accesscategory having two priorities. Background has priorities of 0 and 1,best effort has priorities of 2 and 3, video has priorities of 4 and 5,and voice has priorities of 6 and 7. For each access category, the lowerpriority is for data and the higher priority is for signaling. Thisallows signaling to be sent before data if there is contention betweendata and signaling.

An access point may set the values of AIFS, CWmin, CWmax, and TXOP limitfor each access category. These parameter values may determine thelikelihood of gaining access to the channel, the average duration forchannel access, the average transmission time on the channel, etc. Ingeneral, smaller values for AIFS, CWmin and CWmax may improve channelaccess and may thus be used for data and signaling in higher priorityaccess categories. The access point may transmit the access parametervalues in beacon frames, probe response frames, association responseframes, etc. All stations associated with the access point may use theaccess parameter values to access the channel.

FIG. 3 shows a message flow 300 for a VoIP call/session by station 110.FIG. 3 shows (i) data and signaling exchanges between station 110 andaccess points 120 a and 120 b and (ii) SIP signaling exchanges betweenstation 110 and an IM core network (IM CN) 190. IM CN 190 may includeCSCF 172 or 174 and possibly other network entities. For simplicity,data and signaling exchanges between access points 120 a and 120 b andother network entities such as PDG/WAG 162 and PDIF 164 are not shown inFIG. 3. Signaling exchanges among various network entities in IM CN 190are also not shown.

Initially, station 110 may search for WLANs, detect access points inWLAN 100, and associate with access point 120 a in WLAN 100 (step M1).Step M1 may include making RSSI measurements, reading beacon frames,exchanging probe request/response, performing access and userauthentication, and exchanging association request/response with accesspoint 120 a. Station 110 may then discover the QoS capability of accesspoint 120 a, e.g., based on beacon frames transmitted periodically byaccess point 120 a, a probe response sent by access point 120 a for aprobe request sent by station 110, etc. (step M2). Station 110 a maythen perform IMS registration with IM CN 190 (step M3). Steps M1 to M3may be performed when station 110 is powered up, when station 110 movesinto a new coverage area, etc.

A VoIP application may be launched at station 110. Station 110 may thenestablish a VoIP call with remote terminal 180, which may be coupled toPSTN 178 as shown in FIG. 1 or some other wireless or wireline network.Station 110 may establish QoS for RTP and SIP flows for the VoIP callwith access point 120 a (step M4). Station 110 may also performed IMSsession establishment with TM CN 190 (step M5). Steps M4 and M5 are forcall setup and may be performed concurrently or in different orderdepending on whether station 110 originated or received the VoIP call.

After completing call setup, station 110 may exchange VoIP data withaccess point 120 a (step M6), which may route the VoIP data to remoteterminal 180 (not shown in FIG. 3). A voice frame may be generated by avoice coder/decoder (vocoder) and sent in an RTP packet. RTP packets maybe encapsulated in UDP datagrams and sent in IP packets. Station 110 mayestablish a traffic stream for the voice access category in step M4. Atany time during the call, station 110 may add a new traffic stream orupdate an existing traffic stream, both of which are referred to as“adding” a traffic stream (step M7). Station 110 may exchange VoIP datawith access point 120 a for all traffic stream(s) (step M8).

Station 110 may perform handoff from access point 120 a to access point120 b during the VoIP call (step M9). Step M9 may include sending adisassociation message to access point 120 a, receiving anacknowledgement from access point 120 a, sending an association requestmessage to access point 120 b, receiving an association response messagefrom access point 120 b, and establishing QoS with access point 120 b.Station 110 may then exchange VoIP data with access point 120 b based onthe QoS granted by access point 120 b (step M10). At some point, station110 or remote terminal 180 may terminate the VoIP call. Station 110 mayexchange SIP signaling with IM CN 190 for IMS session termination (stepM11) and may de-activate QoS for the RTP and SIP flows (step M12). StepsM10 and M11 are for call termination and may be performed concurrentlyor in different order.

Steps M4 through M12 may be performed for another call. Station 110 mayperform IMS de-registration, e.g., when a VoIP application is closed(step M13).

In FIG. 3, each step is represented by a double-headed arrow andtypically involves a set of messages exchanged between at least twoentities. Some of these steps may be performed in a manner such thatimproved performance may be achieved for a call, as described below.

In an aspect, station 110 ensures that an access point in a WLAN is“suitable” prior to performing registration to receive services via theWLAN or to move services over to the WLAN. The channel conditionsbetween station 110 and the access point may fluctuate widely, and thereceived signal quality may likewise vary widely. The access point maybe considered suitable if it is relatively stable and can be receivedwith sufficient signal quality by station 110. Station 110 may delayservice registration until station 110 determines that the access pointis suitable. This delayed service registration may avoid a scenario inwhich station 110 performs service registration via an intermittentaccess point and receives poor quality service via this access point.

The suitability of an access point may be determined based on RSSImeasurements, FER for beacon frames, etc. The access point mayperiodically transmit beacon frames, e.g., every 100 milliseconds (ms).In one design, station 110 may make RSSI measurements for the beaconframes received from the access point. Station 110 may compare the RSSImeasurements against an RSSI threshold and declare the access point tobe suitable if a predetermined percentage of the RSSI measurements isabove the RSSI threshold. In another design, station 110 may decode eachreceived beacon frame and determine whether the beacon frame is decodedcorrectly or in error. Station 110 may determine the FER for beaconframes received over a certain time interval, e.g., one to five seconds.Station 110 may compare the beacon FER against an FER threshold (e.g.,10%) and may declare the access point to be suitable if the beacon FERis below the FER threshold. In another design, station 110 may firstmake RSSI measurements for the access point. If some number of RSSImeasurements exceed the RSSI threshold, then station 110 may nextascertain the beacon FER to determine whether the access point issuitable. Station 110 may also determine whether the access point issuitable based on other parameters.

Station 110 may perform service registration after identifying asuitable access point in the WLAN. Station 110 may register in IMS toreceive all services via the WLAN. Alternatively, station 110 mayregister in IMS to receive only certain services via the WLAN, e.g.,depending on the performance of the WLAN and the QoS requirements of theservices. For example, station 110 may register to receive best effortservices via the WLAN if the beacon FER is below a first FER threshold.Station 110 may register to receive VoIP service via the WLAN if thebeacon FER is below a second FER threshold that is lower than the firstFER threshold. Correspondingly, Station 110 may de-register for the besteffort service if the beacon FER exceeds a third FER threshold that ishigher than the first FER threshold. Station 110 may de-register for theVoIP service if the beacon FER exceeds a fourth FER threshold that ishigher than the second FER threshold. For each service, the FERthreshold for registration may be lower than the FER threshold forde-registration in order to provide hysteresis and avoid ping-pong inthe WLAN selected for the service. The beacon FER may be filtered toobtain more reliable FER measurements. Station 110 may thus separateradio acquisition for the WLAN and IMS registration to receive servicesvia the WLAN.

Station 110 may also change service registration based on theperformance of the WLAN. For example, station 110 may initially registerin IMS to receive all services via the WLAN. If the WLAN performancedegrades, then station 110 may de-register with IMS for VoIP service butmay continue to receive best effort service via the WLAN. The WLANperformance may be quantified by RSSI measurements, beacon FER, dataPER, etc.

FIG. 4 shows a design of a process 400 performed by station 110 forservice registration. Station 110 may detect for access points in a WLAN(block 412). Station 110 may determine whether any detected access pointis suitable for receiving service (block 414). Station 110 may determinethat an access point is suitable for receiving service if (i) a FER forbeacon frames received from the access point is below an FER thresholdand/or (ii) a particular percentage of RSSI measurements for the accesspoint is above an RSSI threshold. Station 110 may determine that anaccess point is suitable for receiving service based on measurementsobtained for the access point for a sufficiently long time period (e.g.,more than one second) to ensure that the access point is stable.

Station 110 may perform service registration after determining asuitable access point for receiving service (block 416). The serviceregistration is typically with a designated network entity in anappropriate network, which may be a home network, a visited network, orsome other network. For example, station 110 may register with a P-CSCFfor IMS, with a home agent for mobile IP, etc. Station 110 may alsoregister for different services depending on performance. For example,station 110 may register for best effort service if the FER for thesuitable access point is below a first FER threshold and register forVoIP service if the FER is below a second FER threshold that is lowerthan the first FER threshold.

In another aspect, station 110 may first request for radio resources fortraffic flows and then request for radio resources for signaling flows.For a VoIP call, station 110 may first request radio resources for anRTP flow and may then request radio resources for a SIP flow. Thetraffic flows may have QoS requirements for satisfactory performance.Radio resources may be requested to ensure that the required QoS can beachieved for these traffic flows. The signaling flows may be able totolerate delay and may be sent as best effort traffic if no radioresources are granted for these flows. This manner of requesting forradio resources for traffic and signaling flows may allow the call toproceed when radio resources are granted for the traffic flows but notfor the signaling flows.

Radio resources may also be referred to as air-link resources, QoSresources, resources, etc. Radio resources may be quantified indifferent manners for different wireless networks. Radio resources mayalso be granted in different manners for different wireless networks anddifferent operating modes of a given wireless network. For WLAN, radioresources may be quantified by time (and also by transmit power to alesser extent). IEEE 802.11e supports a scheduled Automatic Power SaveDelivery (S-APSD) mode and an unscheduled APSD (U-APSD) mode. In theS-APSD mode, an access point schedules service times for stationsassociated with that access point. The access point may grant radioresources based on the duration and periodicity of the services timesscheduled by the access point. In the U-APSD mode, each station mayindependently choose its service times, and the access point buffersdata for the station. Regardless of the mode of operation, the accesspoint may grant radio resources to each station in order to meet the QoSrequirements of that station.

The access point may have knowledge of the traffic streams and QoSrequirements of all stations associated with that access point. Theaccess point may be able to grant or deny requests for radio resourcesfrom the stations based on the radio resources available to the accesspoint and the radio resources allocated to the stations. Radio resourcesare related to QoS, and the two terms are often used interchangeably.

FIG. 5 shows a message flow 500 for mobile-originated call setup.Message flow 500 may be used for steps M4 and M5 in FIG. 3. Initially,VoIP call setup for a VoIP call may be triggered, e.g., in response to auser dialing a number at station 110 (step A1). An RTP flow for the VoIPcall may be activated, and a VoIP application (APP) 112 at station 110may send a request for QoS for the RTP flow to a call processing (Proc)module 114 within station 110 (also step A1). Station 110 may then sendto access point 120 a an ADDTS (Add Traffic Stream) Request message thatincludes the requested QoS for the RTP flow (step A2). The RTP flow maybelong in the voice access category (AC_VO). The ADDTS Request messagemay request addition of a traffic stream for the voice access categoryand may include a TSPEC for this access category. The TSPEC may containparameters describing the requested QoS for the RTP flow. Access point120 a may grant radio resources for the requested QoS and may return anADDTS Response message that indicates the grant of radio resources (stepA3). Module 114 may receive the ADDTS Response message and send a QoSactivated notification for the RTP flow to VoIP application 112 (stepA4).

A SIP flow for the VoIP call may then be activated, and VoIP application112 may send a request for QoS for the SIP flow to module 114 (step A5).The RTP and SIP flows may be for the same voice access category. Module114 may then aggregate the required QoS for the SIP flow with therequired QoS for the RTP flow to obtain the aggregated QoS for the voiceaccess category. Station 110 may then send to access point 120 a anADDTS Request message that includes parameters describing the aggregatedQoS for both the RTP and SIP flows (step A6). Access point 120 a maygrant radio resources for the aggregated QoS for both flows and mayreturn an ADDTS Response message that indicates the grant of radioresources (step A7). Module 114 may receive the ADDTS Response messageand send a QoS activated notification for the SIP flow to VoIPapplication 112 (step A8). Station 110 may then send SIP signaling(e.g., a SIP Invite message) as QoS traffic for the voice accesscategory (step A9).

If access point 110 a does not have sufficient radio resources for theaggregated QoS for both the RTP and SIP flows, then in step A7 accesspoint 110 a may return an ADDTS Response message with an indication ofrejection of the aggregated QoS request. Module 114 may then provide afailure notification to VoIP application 112 in step A8. Station 110 maythen send SIP signaling as best effort traffic starting in step A9 andmay proceed with call setup.

If access point 110 a does not have sufficient radio resources for theRTP flow, then in step A3 access point 110 a may return an ADDTSResponse message with an indication of rejection of the QoS request.Module 114 may then provide a failure notification to VoIP application112 in step A4. If QoS for the RTP flow is preferred but not required,then station 110 may proceed with the VoIP call and may send RTP dataand SIP signaling as best effort traffic. If QoS for the RTP flow isrequired, then the VoIP call would fail with access point 120 a, andstation 110 may attempt the call on another wireless network, e.g., 3GPPnetwork 102 or 3GPP2 network 104 in FIG. 1.

FIG. 6 shows a message flow 600 for mobile-terminated call setup.Message flow 600 may also be used for steps M4 and M5 in FIG. 3.Initially, station 110 may receive a SIP Invite message from remoteterminal 180 for an incoming call (step B1). VoIP call setup may betriggered by the SIP Invite message (step B2). Steps B2 through B9 maythen be performed in similar manner as steps A1 through A8,respectively, in FIG. 5. Station 110 may then send a SIP 1xx Responsemessage (e.g., a SIP 180 Ringing message) using the granted radioresources for the voice access category if the QoS request for the SIPflow is granted by access point 120 a in step B8. Alternatively, the SIPmessage may be sent as best effort traffic if the QoS request for theSIP flow is not granted.

Station 110 may send RTP data and SIP signaling for the VoIP call. Thedata and signaling may be exchanged with the WLAN and may achieve thedesired QoS with the radio resources granted by the WLAN. The data andsignaling may be forwarded to nodes outsides of the WLAN to remoteterminal 180. Station 110 may use differentiated service marking toachieve good performance for the data and signaling for the VoIP call.In IP version 4 (IPv4), each IP packet includes a header having an 8-bitType of Service (TOS) field. The TOS field is divided into a 6-bitDifferentiated Services Codepoint (DSCP) field and a 2-bit currentlyunused (CU) field. Various values are defined for the DSCP field fordifferent services. Packets may be classified and marked as belonging ina particular service. These packets may then receive designated per-hopforwarding behavior on nodes along their paths. Packets for VoIP may bemarked with an octal value of 56 to receive expedited forwarding bynodes that support differentiated services.

FIG. 7 shows a design of a process 800 performed by station 110 torequest radio resources. Station 110 may request for radio resources forat least one traffic flow, e.g., an RTP flow (block 712). Station 110may receive a first grant of radio resources for the at least onetraffic flow (block 714). Station 110 may then request for radioresources for at least one signaling flow, e.g., a SIP flow, afterreceiving the first grant (block 716). Station 110 may communicate viathe at least one traffic flow and the at least one signaling flowregardless of whether or not radio resources are granted for the atleast one signaling flow (block 718).

Station 110 may send data for the at least one traffic flow with thefirst grant of radio resources. If station 110 receives a second grantof radio resources for the at least one signaling flow, then station 110may send signaling for the at least one signaling flow with the secondgrant of radio resources. If station 110 receives no grant of radioresources for the at least one signaling flow, then station 110 may sendsignaling for the at least one signaling flow as best effort traffic.Station 110 may send data for the at least one traffic flow andsignaling for the at least one signaling flow with expedited forwardingbased on DSCP marking for packets carrying the data and signaling.

The traffic and signaling flows may be for the same access category,e.g., voice. Station 110 may send data for the at least one traffic flowbased on the AIFS, CWmin, CWmax, and TXOP limit values for this accesscategory. Station 110 may send signaling for the at least one signalingflow based on the AIFS, CWmin, CWmax, and TXOP limit values for thisaccess category (if radio resources are granted) or based on the AIFS,CWmin, CWmax, and TXOP limit values for the best effort access category(if radio resources are not granted).

In yet another aspect, station 110 may aggregate QoS requirements andrequest QoS for each access category. Station 110 may have any number ofactive applications, which may have any number of flows for any set ofaccess categories. Station 110 may aggregate the QoS requirements forall applications for each access category. In one design, the QoS fortraffic flows (but not signaling flows) for each access category isaggregated. In another design, the QoS for traffic flows for each accesscategory is aggregated, and the QoS for signaling flows for each accesscategory is aggregated separately. In yet another design, the QoS forboth traffic and signaling flows for each access category is aggregated.In any case, station 110 may request for radio resources for theaggregated QoS for each access category.

The QoS for a given application may be quantified by parameters such asdelay bound, throughput, PER, and jitter. Multiple applications may befor the same access category (e.g., voice) and may have the same ordifferent values for these QoS parameters. For example, N applications 1to N for a given access category may have delay bound requirements of D₁to D_(N), respectively, throughput requirements of T₁ to T_(N), PERrequirements of PER₁ to PER_(N), and jitter requirements of J₁ to J_(N).The QoS for these N applications may be aggregated by taking thesmallest of the N delay bound requirements, the sum of the N throughputrequirements, the smallest of the N PER requirements, and the smallestof the N jitter requirements for these N applications. The aggregatedQoS may then be requested for these N applications.

For a given access category, a new application may be added to thataccess category at any time, and an existing application may be removedfrom the access category at any time. Whenever an application is addedto or removed from the access category, the aggregated QoS for theaccess category may be updated based on the QoS of the added or removedapplication. Station 110 may then request for radio resources for theupdated aggregated QoS from the WLAN by sending an ADDTS Request messagewith a new TSPEC for the updated aggregated QoS. The WLAN may grant therequest and return an ADDTS Response message. The WLAN may also deny therequest, in which case the new TSPEC is not supported by the WLAN butthe prior TSPEC is still applicable. After the last application for theaccess category is closed, station 110 may delete the traffic stream forthis access category by sending a DELTS (Delete Traffic Stream) Requestmessage.

The aggregation of QoS for all applications in each access category maybe performed at the start of a call prior to QoS establishment in stepM4 in FIG. 3. The aggregated QoS may then be requested from the WLAN instep M4. The aggregated QoS may also be updated during the call whenevera new application is added or an existing application is closed. Theupdated aggregated QoS may then be requested from the WLAN, e.g., instep M7 in FIG. 3.

FIG. 8 shows a design of a process 800 performed by station 110 toaggregate QoS for multiple applications. Station 110 may determine QoSfor each of multiple applications (block 812) and may aggregate the QoSfor the multiple applications (block 814). Station 110 may request forradio resources from a WLAN based on the aggregated QoS for the multipleapplications (block 816).

Thereafter, station 110 may determine QoS for an additional application(block 818) and may update the aggregated QoS with the QoS for theadditional application (block 820). Station 110 may then request forradio resources based on the updated aggregated QoS (block 822). Station110 may determine QoS for one of the multiple applications being closed(block 824) and may update the aggregated QoS with the QoS for theapplication being closed (block 826). Station 110 may then request forradio resources based on the updated aggregated QoS (block 828). Themultiple applications may be for the same access category. Station 110may send data and/or signaling for these applications based on the AIFS,CWmin, CWmax, and TXOP limit values for this access category.

Station 110 may establish a traffic stream for the multiple applicationswith the WLAN. Station 110 may update the aggregated QoS for themultiple applications whenever an additional application is added or anexisting application is closed. Station 110 may then send an ADDTSRequest message with updated parameter values (e.g., an updated TSPEC)determined based on the updated aggregated QoS. Station 110 may alsosend a DELTS Request message when the last of the multiple applicationsis closed.

In yet another aspect, station 110 may relinquish extra radio resourcesif the QoS granted to station 110 for a call is greater than the QoSsupported by remote terminal 180 for the call. Station 110 may begranted certain QoS by the WLAN in step M4. Station 110 may performend-to-end QoS negotiation with terminal 180 in step M5 to determine theQoS for the call. If the QoS negotiated with terminal 180 is lower thanthe QoS granted by the WLAN, then station 110 may relinquish extra radioresources corresponding to the difference between the QoS granted by theWLAN and the QoS negotiated with terminal 180.

For a mobile-originated VoIP call, e.g., as shown in FIG. 5, station 110may send a SIP Invite message to terminal 180 during the IMS sessionestablishment. This

SIP Invite message may include one or more media formats supported bystation 110, which may be given in an order of preference by station110. Each media format may be associated with a set of parameters to usefor communication and may also be associated with a particular QoS. ForVoIP, each media format may correspond to a set of vocoders and aparticular QoS level or profile. The media format(s) supported bystation 110 may be determined based on the QoS granted to station 110 bythe WLAN. For example, QoS levels A through Z may be available, with QoSlevel A being the highest and QoS level Z being the lowest. Station 110may request for QoS level B from the WLAN, and the WLAN may grant QoSlevel D to station 110. The media format(s) included in the SIP Invitemessage may then be associated with QoS level D or lower.

Remote terminal 180 may also request for radio resources, e.g., uponreceiving the SIP Invite message from station 110. Terminal 180 may thenreturn a SIP 180 Ringing message that may include one or more mediaformats supported by terminal 180, which may be given in an order ofpreference by terminal 180. The media format(s) supported by terminal180 may be determined based on the QoS granted to terminal 180. Forexample, the most preferred media format from station 110 may requireQoS level D, terminal 180 may then request for QoS level D but may begranted QoS level E. The media format(s) included in the SIP 180 Ringingmessage may then be associated with QoS level E or lower.

Station 110 may communicate with terminal 180 based on the mostpreferred media format supported by both entities. If this selectedmedia format requires certain QoS that is lower than the QoS granted tostation 110 by the WLAN, then station 110 may release the extra radioresources corresponding to the difference between the QoS granted tostation 110 and the QoS for the selected media format. Station 110 maycommunicate with terminal 180 using the selected media format.

For a mobile-terminated VoIP call, e.g., as shown in FIG. 6, station 110may receive a SIP Invite message from terminal 180 during the IMSsession establishment. This SIP Invite message may contain one or moremedia formats supported by terminal 180. Station 110 may request for QoSfrom the WLAN and may be granted certain QoS by the WLAN. The grantedQoS may be higher than the highest QoS for the media format(s) proposedby terminal 180. If station 110 proposes a media format with QoS higherthan the highest QoS from terminal 180, then there is high likelihood ofthis media format being rejected by terminal 180. Station 110 may thusrestrict the media format(s) proposed to terminal 180 to those with QoSequal to or lower than the highest QoS from terminal 180. For example,the media format(s) proposed by terminal 180 may be associated with QoSlevel E or lower. Station 110 may be granted QoS level B by the WLAN butmay propose media format(s) with QoS level E or lower. The media formatselected for use by station 110 and terminal 180 may have QoS level E orlower. Station 110 may then relinquish the extra radio resourcescorresponding to the difference between the QoS granted by the WLAN andthe QoS negotiated with terminal 180.

FIG. 9 shows a design of a process 900 performed by station 110 torelinquish extra radio resources. Station 110 may determine QoS grantedby a WLAN (block 912) and may determine QoS for a media format proposedby a remote terminal for a call (block 914). Station 110 may releaseextra radio resources corresponding to the difference between the QoSgranted by the WLAN and the QoS for the media format proposed by theremote terminal (block 916).

For a mobile-originated call, station 110 may determine at least onemedia format based on the QoS granted by the WLAN, with each mediaformat being associated with QoS equal to or lower than the QoS grantedby the WLAN. Station 110 may then send the at least one media format asproposal to the remote terminal. The media format proposed by the remoteterminal may be one of the media format(s) sent by station 110.

For a mobile-terminated call, station 110 may select a media formatbased on the QoS for the media format proposed by the remote terminal.The media format selected by station 110 may be associated with QoSequal to or lower than the QoS for the media format proposed by theremote terminal. Station 110 may then send the selected media format tothe remote terminal. Station 110 may release extra radio resourcescorresponding to the difference between the QoS granted by the WLAN andthe QoS for the media format sent to the remote terminal.

As shown in FIG. 3, station 110 may be handed off from current accesspoint 120 a to new access point 120 b during the VoIP call. Station 110may communicate with remote terminal 180 based on a particular QoSgranted by access point 120 a. Station 110 may request the same orhigher QoS from new access point 120 b, which may be able to granthigher QoS than current access point 120 a. Station 110 may receive agrant of higher QoS from new access point 120 b and may propose thehigher QoS to remote terminal 180. In this case, terminal 180 may needto re-negotiate QoS with its network for the higher QoS, which may theninterrupt the current call.

In yet another aspect, when handed off from current access point 120 ato new access point 120 b, station 110 may request for QoS from the newaccess point based on the QoS granted by the current access point. TheQoS granted by current access point 120 a may or may not be the QoSoriginally requested by station 110. For example, station 110 mayoriginally request for QoS level A from current access point 120 a butmay be granted QoS level D. Station 110 may communicate with remoteterminal 180 based on QoS level D granted by current access point 120 a.When handed off to new access point 120 b, station 110 may request QoSlevel D (instead of QoS level A) from the new access point. Thelikelihood of being granted QoS level D may be greater than thelikelihood of being granted QoS level A. If station 110 is granted QoSlevel D, then station 110 may continue to communicate with remoteterminal 180 using QoS level D, without the need for QoS re-negotiationby remote terminal 180. If station 110 is granted a QoS level lower thanQoS level D, then station 110 may continue to communicate with remoteterminal 180 using the lower QoS level. Remote terminal 180 mayrelinquish the extra radio resources corresponding to the differencebetween QoS level D and the lower QoS level.

FIG. 10 shows a design of a process 1000 performed by station 110 toestablish QoS with a new access point during handoff. Station 110 mayrequest for QoS from a first access point in a WLAN (block 1012) and mayreceive a grant of a first QoS from the first access point (block 1014).The first QoS may be equal to or lower than the QoS requested from thefirst access point. Station 110 may communicate with a remote terminalbased on the first QoS granted by the first access point (block 1016).Station 110 may perform handoff from the first access point to a secondaccess point (block 1018). Station 110 may request for the first QoS orlower from the second access point (block 1020) and may receive a grantof the first QoS or lower from the second access point (block 1022).Station 110 may then communicate with the remote terminal based on thefirst QoS or lower granted by the second access point (block 1024).

Data performance for station 110 may degrade during a call, e.g., due tocongestion in the WLAN. Station 110 may then operate with lower QoS(e.g., use lower data rate for the vocoder) and may request for thelower QoS from the access point. This may alleviate congestion in theWLAN.

In yet another aspect, station 110 may first attempt to place anemergency call with a cellular network when a user dials an emergencynumber such as 911 in the United States or 112 in Europe. Station 110may attempt to establish a circuit-switched call and/or apacket-switched call for the emergency call, depending on the capabilityof the cellular network and station 110. If the emergency call fails onthe cellular network, then station 110 may attempt to place theemergency call with a WLAN.

It may be desirable to have the emergency call with the cellularnetwork, if available, since the cellular network may have positioningcapabilities and may be able to determine the location of station 110.However, if the cellular network is not available, then it may bedesirable to have the emergency call with the WLAN.

After terminating the emergency call, whether placed in the cellularnetwork or the WLAN, station 110 may remain in a callback state for apredetermined time period. During this period, station 110 may monitorthe cellular network on which the emergency call was originally placedor any network that is available for emergency call. This callback modeallows a public agency (e.g., law enforcement) to reach station 110 tolocate the user and/or for other tasks.

FIG. 11 shows a design of a process 1100 performed by station 110 toplace an emergency call. Station 110 may receive an indication to placean emergency call, e.g., in response to a user dialing an emergencynumber (block 1112). Station 110 may place the emergency call (e.g., acircuit-switched call and/or a packet-switched call) with a cellularnetwork in response to the indication (block 1114). Station 110 mayplace the emergency call (e.g., a VoIP call) with a WLAN if theemergency call is not successfully placed with the cellular network(block 1116).

FIG. 12 shows a block diagram of a design of station 110, which may becapable of communicating with access points in WLANs and base stationsin WWANs, e.g., cellular networks. On the transmit path, data andsignaling to be sent by station 110 is processed (e.g., formatted,encoded, and interleaved) by an encoder 1222 and further processed(e.g., modulated and scrambled) by a modulator (Mod) 1224 to generateoutput chips. The processing by encoder 1222 and modulator 1224 isdependent on the radio technology (e.g., 802.11, cdma2000, GSM, W-CDMA,etc.) for the wireless network to which data and signaling are sent. Atransmitter (TMTR) 1232 conditions (e.g., converts to analog, filters,amplifies, and frequency upconverts) the output chips and generates aradio frequency (RF) output signal, which is transmitted via an antenna1234.

On the receive path, RF signals transmitted by access points in WLANsand/or base stations in WWANs are received by antenna 1234 and providedto a receiver (RCVR) 1236. Receiver 1236 conditions (e.g., filters,amplifies, frequency downconverts, and digitizes) the received RF signaland provides samples. A demodulator (Demod) 1226 processes (e.g.,descrambles and demodulates) the samples to obtain symbol estimates. Adecoder 1228 processes (e.g., deinterleaves and decodes) the symbolestimates to obtain decoded data and signaling. The processing bydemodulator 1226 and decoder 1228 is complementary to the processing bythe modulator and encoder at the access point or base station beingreceived. Encoder 1222, modulator 1224, demodulator 1226 and decoder1228 may be implemented by a modem processor 1220.

A controller/processor 1240 directs the operation of various processingunits at station 110. Memory 1242 stores program codes and data forstation 110. Controller/processor 1240 may implement or direct processes400, 700, 800, 900, 1000 and/or 1100 in FIGS. 4, 7, 8, 9, 10 and 11,respectively, message flows 300, 500 and/or 600 in FIGS. 3, 5 and 6,respectively, and/or other processes and message flows to supportcommunication for station 110. Memory 1242 may store information for QoSfor different flows and applications, access parameter values for eachaccess category, and/or other information.

The techniques described herein may be implemented by various means. Forexample, these techniques may be implemented in hardware, firmware,software, or a combination thereof. For a hardware implementation, theprocessing units used to perform the techniques may be implementedwithin one or more application specific integrated circuits (ASICs),digital signal processors (DSPs), digital signal processing devices(DSPDs), programmable logic devices (PLDs), field programmable gatearrays (FPGAs), processors, controllers, micro-controllers,microprocessors, electronic devices, other electronic units designed toperform the functions described herein, a computer, or a combinationthereof.

For a firmware and/or software implementation, the techniques may beimplemented with modules (e.g., procedures, functions, etc.) thatperform the functions described herein. The firmware and/or softwareinstructions may be stored in a memory (e.g., memory 1242 in FIG. 12)and executed by a processor (e.g., processor 1240). The memory may beimplemented within the processor or external to the processor. Thefirmware and/or software instructions may also be stored in otherprocessor-readable medium such as random access memory (RAM), read-onlymemory (ROM), non-volatile random access memory (NVRAM), programmableread-only memory (PROM), electrically erasable PROM (EEPROM), FLASHmemory, compact disc (CD), magnetic or optical data storage device, etc.

An apparatus implementing the techniques described herein may be astand-alone unit or may be part of a device. The device may be (i) astand-alone integrated circuit (IC), (ii) a set of one or more ICs thatmay include memory ICs for storing data and/or instructions, (iii) anASIC such as a mobile station modem (MSM), (iv) a module that may beembedded within other devices, (v) a cellular phone, wireless device,handset, or mobile unit, (vi) etc.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the spirit or scopeof the disclosure. Thus, the disclosure is not intended to be limited tothe examples and designs described herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. An apparatus, comprising: at least one processorconfigured to detect one or more access points in a wireless local areanetwork (WLAN), to determine whether any detected access point issuitable for receiving service, to perform service registration with asuitable access point in the WLAN, wherein the service registration isfor a first set of services depending on performance of the suitableaccess point and Quality of Service (QoS) requirements of the first setof services, to establish a communication call that is supported by thefirst set of services associated with the service registration, todetermine either that (i) the performance of the suitable access pointhas changed so as to be different, or (ii) a handoff to a differentaccess point with different performance than the suitable access pointhas occurred, to modify the service registration to a second set ofservices based on the performance difference determination, and totransition, in response to the modification, from supporting thecommunication call using the first set of services to the second set ofservices, wherein the first and second sets of services includedifferent tiers of QoS support for supporting the communication call;and a memory coupled to the at least one processor.
 2. The apparatus ofclaim 1, wherein the at least one processor is configured to determinethat a given access point is suitable for receiving service if a frameerror rate (FER) for beacon frames received from the given access pointis below an FER threshold.
 3. The apparatus of claim 1, wherein the atleast one processor is configured to determine that a given access pointis suitable for receiving service if a particular percentage of receivedsignal strength indicator (RSSI) measurements for the given access pointis above an RSSI threshold.
 4. The apparatus of claim 1, wherein the atleast one processor is configured to determine that a given access pointis suitable for receiving service based on measurements obtained for thegiven access point for a time period longer than one second.
 5. Theapparatus of claim 1, wherein the at least one processor is configuredto register for best effort service if a frame error rate (FER) for thesuitable access point is below a first FER threshold, and to registerfor Voice-over-Internet Protocol (VoIP) service if the FER for thesuitable access point is below a second FER threshold lower than thefirst FER threshold.
 6. The apparatus of claim 5, wherein the at leastone processor is configured to de-register for the best effort serviceif the FER for the suitable access point exceeds a third FER thresholdhigher than the first FER threshold, and to de-register for the VoIPservice if the FER for the suitable access point exceeds a fourth FERthreshold higher than the second FER threshold.
 7. The apparatus ofclaim 1, wherein the at least one processor is configured to perform theservice registration by registering with an IP Multimedia Subsystem(IMS).
 8. A method, comprising: detecting one or more access points in awireless local area network (WLAN); determining whether any detectedaccess point in the WLAN is suitable for receiving service; performingservice registration with a suitable access point, wherein the serviceregistration is for a first set of services depending on performance ofthe suitable access point and Quality of Service (QoS) requirements ofthe first set of services; establishing a communication call that issupported by the first set of services associated with the serviceregistration; determining either that (i) the performance of thesuitable access point has changed so as to be different, or (ii) ahandoff to a different access point with different performance than thesuitable access point has occurred; modifying the service registrationto a second set of services based on the performance differencedetermination; and transitioning, in response to the modifying, fromsupporting the communication call using the first set of services to thesecond set of services, wherein the first and second sets of servicesinclude different tiers of QoS support for supporting the communicationcall.
 9. The method of claim 8, wherein the determining whether anydetected access point is suitable for receiving service comprisesdetermining that a given access point is suitable for receiving serviceif a frame error rate (FER) for beacon frames received from the givenaccess point is below an FER threshold.
 10. The method of claim 8,wherein the performing service registration comprises registering forbest effort service if a frame error rate (FER) for the suitable accesspoint is below a first FER threshold, and registering forVoice-over-Internet Protocol (VoIP) service if the FER for the suitableaccess point is below a second FER threshold lower than the first FERthreshold.
 11. An apparatus, comprising: means for detecting one or moreaccess points in a wireless local area network (WLAN); means fordetermining whether any detected access point is suitable for receivingservice; means for performing service registration with a suitableaccess point in the WLAN, wherein the service registration is for afirst set of services depending on performance of the suitable accesspoint and Quality of Service (QoS) requirements of the first set ofservices; means for establishing a communication call that is supportedby the first set of services associated with the service registration;means for determining either that (i) the performance of the suitableaccess point has changed so as to be different, or (ii) a handoff to adifferent access point with different performance than the suitableaccess point has occurred; means for modifying the service registrationto a second set of services based on the performance differencedetermination; and means for transitioning, in response to themodification, from supporting the communication call using the first setof services to the second set of services, wherein the first and secondsets of services include different tiers of QoS support for supportingthe communication call.
 12. The apparatus of claim 11, wherein the meansfor determining whether any detected access point is suitable forreceiving service comprises means for determining that a given accesspoint is suitable for receiving service if a frame error rate (FER) forbeacon frames received from the given access point is below an FERthreshold.
 13. The apparatus of claim 11, wherein the means forperforming service registration comprises means for registering for besteffort service if a frame error rate (FER) for the suitable access pointis below a first FER threshold, and means for registering forVoice-over-Internet Protocol (VoIP) service if the FER for the suitableaccess point is below a second FER threshold lower than the first FERthreshold.
 14. A non-transitory computer-readable medium includingmachine-executable code configured to cause a machine to performoperations for wireless communication, the machine-executable codecomprising: code for detecting one or more access points in a wirelesslocal area network (WLAN); code for determining whether any detectedaccess point is suitable for receiving service; code for performingservice registration with a suitable access point in the WLAN, whereinthe service registration is for a first set of services depending onperformance of the suitable access point and Quality of Service (QoS)requirements of the first set of services; and code for establishing acommunication call that is supported by the first set of servicesassociated with the service registration; code for determining eitherthat (i) the performance of the suitable access point has changed so asto be different, or (ii) a handoff to a different access point withdifferent performance than the suitable access point has occurred; codefor modifying the service registration to a second set of services basedon the performance difference determination; and code for transitioning,in response to the modification, from supporting the communication callusing the first set of services to the second set of services, whereinthe first and second sets of services include different tiers of QoSsupport for supporting the communication call.
 15. The non-transitorycomputer-readable medium of claim 14, wherein the code for determiningwhether any detected access point is suitable for receiving servicecomprises code for determining that a given access point is suitable forreceiving service if a frame error rate (FER) for beacon frames receivedfrom the given access point is below an FER threshold.
 16. Thenon-transitory computer-readable medium of claim 14, wherein the codefor performing service registration comprises code for registering forbest effort service if a frame error rate (FER) for the suitable accesspoint is below a first FER threshold, and code for registering forVoice-over-Internet Protocol (VoIP) service if the FER for the suitableaccess point is below a second FER threshold lower than the first FERthreshold.
 17. The apparatus of claim 1, wherein the at least oneprocessor is further configured to assess the performance of thesuitable access point and to identify the QoS requirements of the firstset of services, prior to performing the service registration, and toselect one or more appropriate services for the service registrationbased on the assessment and the identification.
 18. The apparatus ofclaim 1, wherein the at least one processor is configured to determinethat the suitable access point is suitable for receiving service basedon measurements obtained from the suitable access point, wherein themeasurements are not associated with any service.
 19. The apparatus ofclaim 1, wherein the service registration is performed with a networkserver that is remote from the WLAN and is configured to provide accessto a plurality of services configured to support communication calls atdifferent quality levels, and wherein one or more services from theplurality of services are excluded from the service registration basedon the performance of the suitable access point and the QoS requirementsof the one or more excluded services.